International Journal of Engineering Research in Africa Vol. 39

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Authors: Ikpe E. Aniekan, Owunna Ikechukwu, Satope Paul
Abstract: Four different riser pipe exit configurations were modelled and the flow across them analysed using STAR CCM+ CFD codes. The analysis was limited to exit configurations because of the length to diameter ratio of riser pipes and the limitations of CFD codes available. Two phase flow analysis of the flow through each of the exit configurations was attempted. The various parameters required for detailed study of the flow were computed. The maximum velocity within the pipe in a two phase flow were determined to 3.42 m/s for an 8 (eight) inch riser pipe. After thorough analysis of the two phase flow regime in each of the individual exit configurations, the third and the fourth exit configurations were seen to have flow properties that ensures easy flow within the production system as well as ensure lower computational cost. Convergence (Iterations), total pressure, static pressure, velocity and pressure drop were used as criteria matrix for selecting ideal riser exit geometry, and the third exit geometry was adjudged the ideal exit geometry of all the geometries. The flow in the third riser exit configuration was modelled as a two phase flow. From the results of the two phase flow analysis, it was concluded that the third riser configuration be used in industrial applications to ensure free flow of crude oil and gas from the oil well during oil production.
Authors: Fatima Ezzahra Saber, Mohamed Ouahi, Abdelmjid Saka
Abstract: This paper introduces a method to estimate the lateral dynamics parameters,which are valuable to the development of more complex and powerful driver assistance system. In the assumption of measured lateral forces, three state observer methods are designed to simultaneously estimate the steering angleas unknown input and vehicle lateral state variables. The stability conditionsof such observers are derived in terms of Linear Matrix Inequalities (LMI). Simulation results through Matlab/Simulink software based on data of the CALLAS vehicle simulator is used to evaluate the performance of observersbased on Unknown Input Observer (OEI).
Authors: Ajibola O. Akinrinde, Andrew Swanson, Remy Tiako
Abstract: Temporary overvoltages caused by primary and secondary islanding due to a fault on a hybrid microgrid of a wind energy and PV system that was connected to the grid, was considered in this study. Symmetry opening of three poles opening and nuisance opening of circuit breaker leading to ferroresonance were investigated using ATP/EMTP. The findings show that during primary islanding an overvoltage of 5.60 P.U. was observed and 7.05 P.U. during secondary islanding. An overvoltage of 3.43 P.U. was experienced during an event of ferroresonance, which could be suppressed by transposing the cable and by connecting a resistive load which is 1% of rated transformer. The effect of the length of the cable on the ferroresonant overvoltage was also studied and found to decrease with the increase of the length of cable.
Authors: V.S. Khoroshilov
Abstract: The research presented in the article is of cutting-edge importance because it proves the necessity to develop prognostic mathematical models with the view to studying the behavior of high-head dams for identifying the regularities of their deformations development process and thus providing quantitative definition for the set criteria values of the diagnostic indices to ensure safe operation of such structures. The paper focuses on the peculiarities of building prognostic mathematical models of the dynamic type on the basis of recurrent equations of the 1st and 2nd orders of different types depending on the order of the mathematical model, number of the principal acting factors and discreteness of the input data, with decorrelation of the input actions and sequence of transport delay introduction. It is shown that the properties of the recurrent equation solution in the form of two first conditional moment generating functions of the displacement process of the observed points in the structure delineate a prognostic model which allows predicting the displacements of the observed points. The paper describes the sequence of estimation stages during the creation of prognostic mathematical models in respect to the character of the predictive problem for various time periods of the structure operation. Different combinations of input actions and discreteness of input data, as well as their decorrelation, have been used. We also applied transport delay in order to correctly consider the inertial delay of the dam under different loads. To account for the residual part of the inertial delay, which is affected by random and unaccounted for factors, we used the autoregression model of the process development regularity. To determine the order of the autoregression model, we calculated asymptotically unbiased ratings of the correlation function for the residual error as a difference between the actual and predicted displacements. Methodological specifics of constructing prognostic models have been established in the context of the factors above. Prognostic mathematical models of different types have been developed for the selected period of the dam operation and the results of prediction have been discussed.
Authors: Zakaria Bouraoui, Sadok Benmebarek, Fernando Lopez-Caballero
Abstract: In this study, a series of nonlinear 2D finite difference analyses were carried out to study the seismic behavior of non-yielding gravity-type earth retaining walls founded in rock site subjected to “Real Near-Fault ground motions”. Numerical analyses were performed by two dimensional explicit FLAC2D finite difference code. Various sets of real data (forty accelerograms) records were applied at the bedrock level to assess model’s dynamic response for different earthquake scenarios. All ground motions have a baseline correction and all output accelerograms obtained from the dynamic analyses are filtered using a non-causal bandpass filter of order 4, between 0.1 and 25 Hz. In these calculations, the foundation non-deformability, the seismic amplification or attenuation and the non-linearity of the soil placed behind the retaining wall are considered. We highlighted an important correlation between the PGA (Pic Ground Acceleration) calculated in free field (accounting for the wave propagation) and the obtained pressure. Numerical results are compared to theoretical calculation methods available in the literature. Among them, Wood's method seems to be the most precise one, presenting small deviations with the numerical methods. Moreover, it is the safest method, in the sense that it predicts the highest pressure values, not only in the elastic cases but even in some situations when non-linearity appears. In addition, we found that the time corresponding to the maximum calculated values of lateral earth pressure acting on the wall matches with the time of the calculated (PGAff). So, the main takeaway of this observation is the zero effect of seismic duration on pressure evolution.
Authors: Benamar Balegh, Habib Trouzine
Abstract: Steel sheet pile wall corrosion in soils and water is a complex phenomenon. The deterioration of these structures is costly and difficult to predict. The aim of this paper was to deal some empirical corrosion models which are analyzed and compared to Eurocode 3, Part 5 to estimate corrosion rate and the loss of thickness of anchored steel sheet pile wall. The results show that care should be taken to ensure that the maximum bending moments do not occur at the same level as the main corrosion zones. Furthermore, it is possible to define an upper and a lower bound, corresponding respectively to the presence of sea water in low water and the undisturbed natural soils, in order to predict the loss of thickness due to corrosion.
Authors: Ayobami Adebola Busari, Isaac I. Akinwumi, Paul O. Awoyera, O.M. Olofinnade, T.I. Tenebe, J.C. Nwanchukwu
Abstract: This experimental research assessed the engineering and geotechnical properties of Aluminum dross (ALDR). Glumly, this solid waste is usually open dumped with detrimental effect on the environment. In a bid to reduce solid waste in the environment and also improve pavement interlayer properties, this research utilized ALDR as a stabilizer for tropical lateritic soil. The lateritic soil was stabilized with the addition of this solid waste at 2% intervals from 2% to 16%. Response surface analysis was used in optimizing the strength and consistency of the stabilized soil sample. The addition of this non-conventional stabilizer helped in modifying the engineering properties of the soil sample, this had indications on the atterberg limit as the liquid limit, and the plasticity index increased from 43% to 54.61% and 28.02%- 40.8% respectively, while the plasticity index reduced from 15.1% - 13.8% signifying soil improvement. The load-bearing capacity of the sample increased from 51.22% to 62.41%. Additionally, the unconfined test showed that addition of ALDR residue improved the consistency of the stabilized soil sample. From the model equation, a positive relationship exists between CBR and UCS. R2 value of 0.81 showed the robustness of the model developed. The research showed that aluminum dross is a suitable material for improving the engineering properties of the tropical lateritic soil towards a sustainable road construction.
Authors: F. Mostefa, Nasr Eddine Bouhamou, H.A. Mesbah, Salima Aggoun, D. Mekhatria
Abstract: This work aims to study the feasibility of making a geopolymer cement based on dredged sediments, from the Fergoug dam (Algeria) and to evaluate their construction potential particularly interesting in the field of special cementitious materials. These sediments due to their mineralogical composition as aluminosilicates; are materials that can be used after heat treatment. Sedimentary clays were characterized before and after calcination by X-ray diffraction, ATG / ATD, spectroscopy (FTIR) and XRF analysis. The calcination was carried out on the raw material sieved at 80 μm for a temperature of 750 ° C, for 3.4 and 5 hours. The reactivity of the calcined products was measured using isothermal calorimetric analysis (DSC) on pastes prepared by mixing an alkaline solution of sodium hydroxide (NaOH) 8 M in an amount allowing to have a Na / Al ratio close to 1 (1: 1). Also, cubic mortar samples were prepared with a ratio L / S: 0.8, sealed and cured for 24 hours at 60 ° C and then at room temperature until the day they were submited to mechanical testing. to check the extent of geopolymerization. The results obtained allowed to optimize the calcination time of 5 hours for a better reactivity of these sediments, and a concentration of 8M of sodium hydroxide and more suitable to have the best mechanical performances.
Authors: Peter Pelumi Ikubanni, Adekunle Akanni Adeleke, Adeolu Adesoji Adediran, Olayinka Oluwole Agboola
Abstract: In this study, particleboard was produced from the blend of sawdust and rice husk with the inclusion of metallic chips and adhesives. Urea formaldehyde and gelatinous starch were used as adhesives. Particleboards (10 mm thickness) were made from varying weight percentage ratio of saw dust and rice husk using pressure in the neighbourhood of 3 N/mm2. The particleboard was tested to determine the density, modulus of rupture (MOR), modulus of elasticity (MOE) and internal bonding strength (IBS). The density of the particleboards developed varies from 762.86 to 801.60 kg/m3. The moisture content of the samples varied between 9.22% and 9.98%. The MOR, MOE and IB values varied between 5.08 MPa and 26.08 MPa; 75.38 MPa and 412.4 MPa; and 0.013 MPa to 0.07 MPa, respectively. Composite samples C, E and H values for MOR, MOE and IBS gave significant results which met with the EN, ANSI A 208.1 and USDA standards. Hence, the admixture of rice husk and sawdust together with UF adhesive will be suitable in producing particleboard that could be useful for indoor and outdoor purposes.
Authors: Getahun Aklilu, Sarp Adali, Glen Bright
Abstract: This paper presents the results of an experimental program to study the mechanical properties of currently available composite materials for the construction of wind turbine blade. The materials identified for this purpose include unidirectional glass fibre/epoxy (GFRP), carbon fibre/epoxy (CFRP) and hybrid combinations of these two materials to be used in a laminated design and at elevated temperatures. The tests conducted in the present programme includes short beam shear test and dynamic mechanical analysis tests after the specimens are exposed to temperatures ranging from 25 to 140°C. The results indicate that the inter-laminar shear failure strength and stiffness of GFRP, CFRP and hybrid specimens degrade with increasing temperature. However, the degradation is observed to be higher in single material specimens in comparison to hybrid specimens. In particular, stiffness of CFRP specimens decreased linearly as the temperature approached 40°C and increased up to the glass transition temperature of epoxy. Experimental results indicated that damping properties of Glass-Carbon-Glass/epoxy specimens improved at elevated temperatures which is important for noise and vibration control. In the present study, empirical models are proposed based on the test data to predict the variation of inter-laminar shear failure stress and stiffness as a function of temperature. The experimental results and proposed model can be used as input parameters to design and construct composite wind turbine blades to be used in tropical wind farms.

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